PIA11675: New Views on Old Finds

These two Cassini images, taken four years before Saturn’s August 2009
equinox, have taken on a new significance as data gathered at equinox
indicate the streaks in these images are likely evidence of impacts into
the planet’s rings.

The images, which were taken 14 minutes apart and have been specially
processed to bring out fine details, show distinct streaks in Saturn’s C
ring. In the left-hand image, the streaks that are nearly horizontal are
background stars elongated by the spacecraft’s motion during the exposure.
(The ring features in these images are not smeared because, in general,
the spacecraft’s camera is turned during imaging exposures to track the
motion of Saturn and its rings.) But the two streaks which are parallel to
the other ring features in the image (one of which intersects a star
trail) and situated in the central bland region of the frame are believed
to be the result of impacts.

The lengths of these features are determined by the impact site’s orbital
motion (from upper right to lower left) during the duration of the
exposure, as well as orbital shear that elongates and tilts (relative to
the orbital direction) the cloud of ejecta. In these images, the former is
much larger than the latter, indicating that these impacts are probably
recent (less than one day old).

These C-ring ejecta clouds are feebler than impacts found during equinox
(see PIA11674), an observation that is
consistent with the impactors being much smaller than 1 meter (3 feet).
The visibility of these faint, narrow features is considerably increased
by the high-phase-angle (171 degrees) viewing conditions, which enhance
the visibility of fine dust.

Together with sightings of streaks in the A and C rings during equinox,
these observations constitute the first visual confirmation of a long-held
belief that bits of interplanetary debris continually rain down on
Saturn’s rings and contribute to the rings’ erosion and evolution.

These two images were processed with a high-pass filter to expose the
streaks, making the rings appear grainier and brighter than in the
original versions. This view looks toward the unilluminated side of the
rings from about 19 degrees above the ring plane.

The images were taken in visible light with the Cassini spacecraft
narrow-angle camera on May 3, 2005. The view was obtained at a distance of
approximately 272,000 kilometers (169,000 miles) from Saturn and at a
Sun-Saturn-spacecraft, or phase, angle of 171 degrees. Image scale is 1
kilometer (4,155 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory,
a division of the California Institute of Technology in Pasadena, manages
the mission for NASA’s Science Mission Directorate, Washington, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.